🧪 Add unit tests for AppTheme.getContrastRatio and fix luminance bug

apps/parable-bloom/lib/core/app_theme.dart

@@ -213,9 +213,9 @@ class AppTheme {
   /// Returns ratio >= 4.5 for normal text, >= 3.0 for large text
   static double getContrastRatio(Color foreground, Color background) {
     double luminance(Color color) {
-      final r = color.r / 255.0;
-      final g = color.g / 255.0;
-      final b = color.b / 255.0;
+      final r = color.r;
+      final g = color.g;
+      final b = color.b;
       final rsRGB = r <= 0.03928 ? r / 12.92 : pow((r + 0.055) / 1.055, 2.4);
       final gsRGB = g <= 0.03928 ? g / 12.92 : pow((g + 0.055) / 1.055, 2.4);
       final bsRGB = b <= 0.03928 ? b / 12.92 : pow((b + 0.055) / 1.055, 2.4);

apps/parable-bloom/test/core/app_theme_test.dart

@@ -0,0 +1,71 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:parable_bloom/core/app_theme.dart';
+
+void main() {
+  group('AppTheme.getContrastRatio Tests', () {
+    test('Pure White vs. Pure Black should have maximum contrast (21.0)', () {
+      final white = Colors.white; // 0xFFFFFFFF
+      final black = Colors.black; // 0xFF000000
+
+      final contrast = AppTheme.getContrastRatio(white, black);
+      expect(contrast, closeTo(21.0, 0.01));
+    });
+
+    test('Same colors should have minimum contrast (1.0)', () {
+      final white = Colors.white;
+      final black = Colors.black;
+      final customColor = const Color(0xFF3A7DAF);
+
+      expect(AppTheme.getContrastRatio(white, white), closeTo(1.0, 0.01));
+      expect(AppTheme.getContrastRatio(black, black), closeTo(1.0, 0.01));
+      expect(AppTheme.getContrastRatio(customColor, customColor),
+          closeTo(1.0, 0.01));
+    });
+
+    test('getContrastRatio is commutative', () {
+      final primary = const Color(0xFF3A7DAF);
+      final background = const Color(0xFFF8F5EF);
+
+      final ratio1 = AppTheme.getContrastRatio(primary, background);
+      final ratio2 = AppTheme.getContrastRatio(background, primary);
+
+      expect(ratio1, equals(ratio2));
+    });
+
+    test('Colors below/above linearization threshold are calculated correctly',
+        () {
+      // Linearization condition: c / 255.0 <= 0.03928
+      // Threshold in 255 range: 0.03928 * 255.0 = 10.0164
+      // So color channel values <= 10 use standard linearization: (c/255.0) / 12.92
+      // Values >= 11 use non-linear formula: pow(((c/255.0) + 0.055) / 1.055, 2.4)
+
+      const veryDarkGray = Color(0xFF090909); // Red, Green, Blue are 9 (<= 10)
+      const slightlyLighterGray =
+          Color(0xFF0B0B0B); // Red, Green, Blue are 11 (>= 11)
+
+      // Both should work and should result in slightly different contrast against white
+      final white = Colors.white;
+
+      final ratioDark = AppTheme.getContrastRatio(veryDarkGray, white);
+      final ratioLighter =
+          AppTheme.getContrastRatio(slightlyLighterGray, white);
+
+      // We expect dark grey to have slightly higher contrast ratio against white than slightly lighter grey
+      expect(ratioDark, greaterThan(ratioLighter));
+    });
+
+    test(
+        'Calculates expected contrast ratios for known WCAG compliancy thresholds',
+        () {
+      // Verify contrast ratio of specific palette colors
+      final primary = const Color(0xFF3A7DAF); // Brand primary blue
+      final lightBg = const Color(0xFFF8F5EF); // Lightened beige background
+
+      final ratio = AppTheme.getContrastRatio(primary, lightBg);
+
+      // Known contrast ratio for #3A7DAF vs #F8F5EF is approx 4.08
+      expect(ratio, closeTo(4.08, 0.05));
+    });
+  });
+}